A non-finite speed ratio transmission device which combines a toroidal continuously variable transmission (CVT), a fixed speed ratio transmission and a planetary gear unit for increasing the speed ratio range of the CVT is disclosed in Tokkai Hei 9-42428 published by the Japanese Patent Office in 1997.
In this device, the engine output is input to both the CVT and a fixed speed ratio transmission. The output shaft of the CVT is joined to a sun gear of the planetary gear unit and an output shaft of the fixed speed ratio transmission is joined to a carrier of planet gears of the planetary gear unit via a power circulation clutch. A ring gear of the planetary gear unit is joined to the drive shaft which drives the wheels. The output shaft of the CVT is also joined to the drive shaft via a direct clutch.
In this device, two power transmission modes are used, i.e., a direct drive mode in which a direct clutch is engaged and a power circulation clutch is disengaged, and a power circulation mode in which the direct clutch is disengaged and the power circulation clutch is engaged.
In the direct mode, the engine output is transmitted to the drive shaft via the CVT. In the power circulation mode, the rotation of the ring gear stops in a position where the rotation of the sun gear which rotates due to the output of the CVT and the rotation of the planet carrier which rotates due to the output of the fixed speed ratio transmission, are balanced. This state is the neutral state where a rotation torque is not transmitted to the drive shaft.
In this case, the ratio of the engine rotation speed and the rotation speed of the drive shaft, i.e., the speed ration of the non-finite speed ratio transmission device, becomes infinite.
This state is called the geared neutral position GNP. Therefore, the rotation direction of the ring gear changes according to whether the speed ratio of the CVT is larger or smaller than the GNP. Forward or reverse motion of the vehicle from stop is therefore performed by increasing or decreasing the speed ratio of the CVT from the GNP.
In this device the speed ratio of the CVT increases as the vehicle speed increases when the vehicle is moving forward in the power circulation mode. Herein the speed ratio of the CVT denotes the ratio of the input rotation speed and output rotation speed of the CVT. When the speed ratio of the CVT has increased to a predetermined speed ratio, the power circulation clutch is disengaged and the direct clutch is engaged.
Hence, there is a change-over from the power circulation mode to the direct mode. In the direct mode, the output of the CVT is directly transmitted to the drive shaft without modification.
Therefore, according to this transmission, all running states including forward and reverse from the stop state of the vehicle, and running at high speed, can be changed over smoothly without using a torque converter. An identical non-finite speed ratio transmission is also disclosed in U.S. Pat. No. 5,935,039.